This invention relates to lightweight aggregates, intermediary aggregates and processes for preparing them.
Since the introduction of cellular or expanded plastic (for example, expanded polystyrene), various researchers have attempted to make practical use of the lightweight and heat insulating properties of this type of plastic in aggregates. However, they have not been put into practical use up to the present time. The hitherto known solutions to this problem have proved to be uneconomical due to the high price of adhesives (for example, synthetic resin adhesives, natural pastes and the like) which have been suggested for adhering the mutually incompatible expanded plastic and cement mortar.
A further problem is the difficulty of mass production due to manufacturing difficulties. Even when the above-mentioned adhesives are used, the following defects remain:
First, the surface of expanded plastic is not easily wettable and therefore they cannot be effectively covered with the conventional adhesives to the required extent resulting in a poor adhesion, and the minute inorganic particles adherent to the adhesive-coated plastic are only thinly covered. The surface layer is therefore weak and can be damaged or broken by friction or impact on the aggregates during curing or transportation.
Secondly, a very long curing time is required for the above-mentioned aggregrates because the adhesives have a tendency to surround the cement particles when the adhesive-coated expanded plastic is being covered with cement mortar, and this inhibits the removals of water and carbon dioxide from the cement during curing.
Thirdly, when the adhesive is dry, the outer layer of cement mortar contracts resulting in serious distortion. These changes reduce the strength of the cement.
Though there has been an effort to mix expanded plastic and cement mortar without using the above-mentioned pastes as adhesive, this has proved impossible except in special cases, because the strength of the matrix is weakened by minute vibrations of the matrix during curing.
The above-mentioned deficiencies have come to light as a result of manufacturing experiments.
In order to avoid these difficulties, it has been found in tests that the use of viscous soils suspended in water as pastes in the formation of an adhesive layer between expanded plastic cores and the cement mortar outer layer is beneficial.